The semiconductor industry is increasingly being driven to decrease the size of semiconductor devices located on integrated circuits. For example, miniaturization is needed to accommodate the increasing density of circuits necessary for today's semiconductor products. The rapid advancement of silicon-based integrated circuit technology brings along the increasingly stringent requirement on the ability of depositing film into spaces having high aspect ratios, e.g. spaces where the ratio of the longest dimension to the shortest dimension is greater than 10. Many semiconductor devices include, for example, vias, gaps, trenches or other structures that contain large aspect ratios that present unique deposition process challenges.
One such problem arises when a space having a large aspect ratio is filled using chemical vapor deposition (CVD) techniques. One example includes trenches having high aspect ratios that are filled using CVD processes. In conventional processes, the trench may be formed with one or more voids or keyholes contained therein. The voids or keyholes are created because the deposition reactants tend to preferentially grow cusps or huts near the vicinity of the entrance (e.g., top portion) of the trench. This results in a greater thickness of the deposited layer near the mouth or opening of the trench compared to the end or bottom. Consequently, the deposited layer nearer the opening of the trench closes or pinches, creating voids or spaces that are left unfilled.
The voids left in semiconductor devices pose a significant problem. For example, voids may result in failure of the device caused by gases (or other materials) contained in the voids. In addition, it is possible that voids may be filled with conductive material during subsequent deposition processes thereby causing shorts in the device components.
U.S. Patent Application No. 2005/0095872 (“Belyansky et al.”) discloses a process for filing high aspect ratio gap filing. According to Belyansky et al., a substrate having gaps to be filled is contacted with a first oxide precursor under high density plasma conditions at a first pressure less than about 10 millitorr, wherein gaps are partially filled with a first oxide material. The substrate is then contacted with a second oxide precursor material and an inert gas under high density plasma conditions at a second pressure greater than 10 millitorr, wherein the gaps are further filled with the second oxide material.
In another aspect, Belyansky et al. discloses a method of depositing a conformal dielectric layer on a substrate disposed in a process chamber wherein a substrate having a gap to be filled is provided on an electrode in the process chamber. An oxide precursor is flowed into the chamber at a pressure less than 10 millitorr to partially fill the gap. The pressure within the chamber is increased to greater than 10 millitorr and an inert gas is flowed into the chamber to fill the gap.
Belyanski et al. thus utilizes a one or two component oxide precursor material utilizing a high density plasma chemical vapor deposition (HDP-CVD) system.
There thus is a need for a CVD-based process for depositing conformal films in high aspect ratio spaces without the use of high density plasma systems. For example, there is a need for a process that utilizes variable pressure (VPCVD) methods that can result in void or keyhole-free fills or films in spaces having aspect ratios higher than 10. For example, there is a need for a method for conformal deposition in spaces having nanometer-sized dimensions with aspect ratios as high as or greater than 10,000.